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Preparation of 2-Methylnaphthalene from 1-Methylnaphthalene Via Catalytic Isomerization and Crystallization

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Preparation of 2-Methylnaphthalene from 1-Methylnaphthalene Via Catalytic Isomerization and Crystallization Available online at BCREC Website: https://bcrec.undip.ac.id Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3) 2018, 512-519 Research Article Preparation of 2-Methylnaphthalene from 1-Methylnaphthalene via Catalytic Isomerization and Crystallization Hao Sun1*, Kang Sun1, Jianchun Jiang1, Zhenggui Gu2 1Jiangsu Key Laboratory for Biomass Energy and Material, National Engineering Laboratory for Biomass Chemical Utilization, Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, Nanjing 210042, China 2Jiangsu Provincial Key Laboratory of Materials Cycling and Pollution Control, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, China Received: 10th May 2018; Revised: 16th July 2018; Accepted: 17th July 2018; Available online: 14th November 2018; Published regularly: December 2018 Abstract Large amounts of residual 1-methylnaphthalene are generated when 2-methylnaphthalene is extracted from alkyl naphthalene. In order to transform waste into assets, this study proposes a feasible process for preparing 2-methylnaphthalene from 1-methylnaphthalene through isomerization and crystalliza- tion. The 1-methylnaphthalene isomerization was carried out in a fixed-bed reactor over mixed acids- treated HBEA zeolite. The results showed that acidic properties of catalysts and reaction temperature were associated with the 2-methylnaphthalene selectivity, yield and catalytic stability. At a high reac- tion temperature of 623 K, the 2-methylnaphthalene yield was 65.84 %, and the deactivation rate was much lower. The separation of reaction products was then investigated by two consecutive crystalliza- tion processes. Under optimal conditions, the 2-methylnaphthalene purity attained 96.67 % in the product, while the yield was 87.48 % in the refining process. Copyright © 2018 BCREC Group. All rights reserved Keywords: Modified zeolite; 1-Methylnaphthalene, Isomerization; Crystallization; 2-Methylnaphthalene How to Cite: Sun, H., Sun, K., Jiang, J., Gu, Z. (2018). Preparation of 2-Methylnaphthalene from 1-Methylnaphthalene via Catalytic Isomerization and Crystallization. Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3): 512-519 (doi:10.9767/bcrec.13.3.2650.512-519) Permalink/DOI: https://doi.org/10.9767/bcrec.13.3.2650.512-519 1. Introduction oil is both inefficient and polluting, because they are made up of about 30 % alkyl naphthalenes. The production of C10 aromatics are the re- Among alkyl naphthalenes, 2-methyl- sidual oils after trimethylbenzene and indane naphthalene (2-MN) is a well-known useful in- are extracted from C9 aromatics, and have termediate for producing polyethylene naphtha- reached more than 300,000 tons per year in lene (PEN) and vitamin K [1-3]. In our previous China. Using C10 aromatics as solvents or fuel study [4], 2-MN was attained from alkyl naph- thalenes via side-stream distillation and * Corresponding Author. continuous crystallization processes. However, E-mail: [email protected] (H. Sun) the residual component was mainly 1-methyl- Telp: +86-25-85482484, Fax: +86-25-85482484 bcrec_2650_2018 Copyright © 2018, BCREC, ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3), 2018, 513 naphthalene (1-MN), the industrial demand for Chemical Regent Co., Ltd., Shanghai, China. which is much lower than that for 2-MN. If we Parent HBEA zeolite was synthesized by the could obtain 2-MN from 1-MN, residual C10 method described in Matsukata et al. [18]. aromatics could be maximally utilized with less waste. 2.2 Catalyst Preparation Past studies [5-11] have demonstrated The parent HBEA zeolite was activated at HBEA zeolite to be an effective catalyst for 823 K (2 K/min heating rate) for 5 h before the 1-MN isomerization owing to its thermal modification. The dealuminated catalyst was stability, appropriate pore size distribution and prepared by impregnating HBEA zeolite into high activity in comparison with those of other 0.1 mol/L solution of mixed hydrochloric and zeolites. However, due to its initial defective oxalic acids (hydrochloric/oxalic = 1) at 343 K structure, detrimental by-products are una- for 1 h. After that, the sample was filtered, voidable during the synthesis process, and its washed, dried and calcined at 823 K (2 K/min catalytic life of isomerization is short. Modifica- heating rate) for 4 h. The synthesized catalyst tions of zeolites, such as: silylation [12], stream was denoted as Mix-HBEA. [13], and dealumination [14-17], are advanta- geous for improving the stability and selectivity 2.3 Characterization of catalytic reaction. Our previous report has studied the HBEA zeolite modified by organic X-ray diffraction (XRD) was recorded on a acid [11], and the modified catalyst demon- D/max-2500 (Rigaku, Japan) using Cu-Kα radi- strated high selectivity for the conversion of al- ation and operating at 100 mA and 40 kV. Fou- kyl naphthalene. Dealumination is accom- rier transform infrared (FTIR) spectroscopy plished by hydrolysis of Al–O–Si bonds with in- was conducted on a Tensor 27 (Bruker, Germa- organic and/or organic acids. It is obvious that ny) spectrometer in the mid-IR region (400- the acids used in the treatment are responsible 4000 cm-1). Surface acidity was performed with for the acidic properties and catalytic perfor- FTIR spectrometry after adsorption of pyridine mance of HBEA zeolite. Nevertheless, the mix- (Py-FTIR), using a Vertex 70 (Bruker, Germa- ture of inorganic and organic acids utilized for ny) spectrometer coupled with a conventional the dealumination of HBEA and the catalytic high vacuum system. The molar extinction co- deactivation rate of mixed acids-treated zeolite efficients for pyridine on the Brönsted (1545 for 1-MN isomerization have scarcely been in- cm-1 band, εB) and Lewis acid sites (1454 cm-1 vestigated. band, εL) were identified as 1.23 cm/μmol and The product of 1-MN isomerization contains 1.73 cm/μmol, respectively [19]. NH3 tempera- both 1-MN and 2-MN due to the thermodyna- ture-programmed desorption (NH3-TPD) was mic equilibrium of isomerization reaction. The carried out on a TP-5080 (Xianquan, China) in- components of this mixture have a large strument equipped with a thermal conductivity difference in melting point, but a small differ- detector. Thermogravimetric (TG) analysis was ence in volatility. As reported in our previous measured using a Diamond TG/DTA (Perkin study [4], crystallization is an effective method Elmer, USA) instrument in the presence of ox- for separating the isomers mixture. ygen. In order to make full use of the 1-MN resul- ting from residual C10 aromatics, this work car- 2.4 Reaction and Separation ried out the 1-MN isomerization over modified The isomerization of 1-MN was performed HBEA zeolite. The modified zeolite was charac- in a fixed-bed reactor. After 1.6 g of catalyst terized by various methods, and its catalytic was loaded in the center of the reactor, the properties were investigated in a fixed-bed re- isomerization was carried out in the presence actor. Furthermore, in order to obtain 2-MN of nitrogen under atmospheric pressure. The with high purity and yield, two-fold crystalliza- flow-rate of 1-MN and N2 were 1.3 h-1 weight tion for the separation of methylnaphthalene hourly space velocity (WHSV) and 20 mL/min, isomers was also studied. respectively. Products were sampled and ana- lyzed at regular intervals. The 1-MN conver- 2. Materials and Methods sion was based on the 1-MN concentration 2.1 Source of Chemicals change, and 2-MN selectivity was defined as the mass ratio of 2-MN to 1-MN conversion. The 1-MN (> 98 % purity) was purchased A home-made apparatus [20] was then uti- from Aladdin Industrial Inc., Shanghai, China. lized to crystallize and filter the products of the Hydrochloric acid and oxalic acid were both isomerization reaction. This apparatus consists analytical regents obtained from Sinopharm Copyright © 2018, BCREC, ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3), 2018, 514 of a jacketed crystallizer, a homothermal filter 3. Results and Discussion and a filtrate collector. The temperature of the 3.1 Characterization of Catalyst apparatus was controlled by a circulating pump, using cold glycol as a cooling medium. The crystal structure and lattice vibration The 2-MN yield in the crystallization process of Mix-HBEA were measured by XRD and was calculated as follows: FTIR, respectively. The XRD results plotted in Figure 1a show typical reflections of the zeolite HBEA at 7.8° and 22.5°, with no other signifi- Ycrystal .C2−MN (1) 2 − MN yield(%) = cant peaks. As shown in Figure 1b, the bands Y 2−MN at 1090 and 795 cm-1 are associated with the symmetric and asymmetric stretching vibra- where Y2-MN is the 2-MN yield in the reaction tions of the TO4 units of zeolite, respectively. process, Ycrystal is the crystal yield of the crystal- At 569 cm-1, the adsorption band represents a lization process, and C2-MN is the 2-MN purity characteristic of the BEA framework structure of the crystal in the crystallization process. in the Mix-HBEA catalyst [21]. These results All samples were quantitatively analyzed by suggest that treatment with mixed acids pre- gas chromatography on a Trace 1300 serves the zeolite structure of HBEA. (ThermoFisher, America) using a SE-30 capil- NH3-TPD analysis was carried out to esti- lary column. A GC-MS (Varian 3800/2200) mated the types and number of acid sites on equipped with a Varian CP-Sil-19 column iden- the surface. The results are depicted in Figure tified the main components as naphthalene 2a. NH3 desorption peaks occurred in the (NA), 1-MN, 2-MN, dimethylnaphthalene ranges of 100-300 °C and 300-700 °C are as- (DMN) and polynuclear aromatic. Figure 1. (a) XRD and (b) FTIR patterns of Mix-HBEA catalyst Figure 2. (a) NH3-TPD curve of Mix-HBEA; (b) FTIR spectra of Mix-HBEA catalyst after desorption of pyridine at 573 K Copyright © 2018, BCREC, ISSN 1978-2993 Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3), 2018, 515 cribed to weakly acidic sites and strongly acidic lower than 573 K and higher than 623 K, sites, respectively [22,23].
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